1. Field
Embodiments of the present disclosure relate to systems and methods for wirelessly monitoring well conditions using high temperature, self-powered, miniature mobile devices including a power generator that generates power based on friction, generated by fluid or mud flow, between two materials of opposite polarity.
2. Description of Related Art
Background
Logging tools, such as wireline logging tools, MWD (measurement while drilling) and LWD (logging while drilling) are used to obtain information about the geological formations both inside and surrounding limited wellbore regions. The information obtained by these downhole measurement tools can be used to make various interpretations about the formations and conditions inside a well, which can then be used to make and revise drilling programs. Wireline and MWD/LWD tools have the ability to measure, either directly or indirectly, a wide range of measurements such as wellbore trajectory, and formation characteristics including resistivity, density, porosity, lithology, mineralogy, geological structure, permeability as well as geomechanical and fluid properties. Wireline tools have been used for many decades to obtain downhole wellbore and formation data.
In a wireline logging operation, a tool which contains several sensors are lowered into a well and data is obtained at various points inside a well until the tool reaches the bottom. Data is also obtained when the wireline tool is pulled out of the well. If the wireline logging tool is to be run for example after drilling an open hole, first, the drilling assembly has to be pulled out of hole. Then, the wireline operation also takes time, depending on the well depth and resolution of the data, to be run in the hole. Once the wireline logging is finished it has to be pulled out of the hole and the drilling assembly has to be run in hole again. Wireline logging is expensive due to the time spent on performing a wireline logging operation as well as the expensive sensors and packaging. During wireline operation, fluid in the wellbore typically remains static and the wellbore condition has to be in a favorable condition, if several logging runs are required, a dedicated wiper trip is required in between logging runs. Moreover, there is always the risk of a wireline logging tool getting stuck in the hole, which could significantly add to the cost of drilling a well.
MWD/LWD tools, as the names suggest, obtain measurements while drilling in real-time. MWD tools are especially important when drilling directional wells since they give the driller information about the trajectory of the well along with information such as tool downhole vibration, and gamma ray tool internal temperature. LWD tools on the other hand obtain information about the geological properties of the well and can be added to a bottom hole assembly depending on the formation evaluation requirements, such as resistivity, density etc. for the primary purpose identifying potential hydrocarbon bearing zone. The signals from the MWD/LWD tools are communicated to the surface by mud pulse telemetry and are recorded at the surface by pressure transducers, which are decoded immediately. MWD/LWD are very expensive, bulky and lengthy tools and mud pulse rate is generally slow (maximum of up to 20 bits/second in the field). The power to the MWD/LWD tools and the mud pulse telemetry unit is provided by batteries and recently by a downhole turbine/alternator. The power generation turbine, if installed close to the mud pulser and above the LWD tool, may prevent the retrieval of radioactive chemical sources in the LWD tool if the drilling bottom-hole assembly gets stuck and cannot be retrieved. It should be pointed out that the MWD/LWD tools are typically placed 35-60 feet away from the drill bit. Therefore, the driller does not have any information about the downhole environment at the bit.
Near-bit tools have gamma ray and inclination sensors 3-10 feet away from the bit but the number of sensors that can be placed near a bit is limited and the sensors are exposed extremely harsh environment, which may affect its performance and lifespan compared to sensor modules located further above the bit. If the drilling assembly contains a mud motor above the near-bit tools, additional data transmission means (data hoop from sensors to mud pulser) are needed to ensure real-time data transmission to surface, which adds considerable technical complexities and therefore prone to problems while operating the tools.